This invention relates to an engine ignition system and more particularly to an engine control unit (ECU) with improved ignition control for an internal combustion engine.
A particularly popular type of engine ignition circuit employs an electronic control for controlling the firing of the spark plugs so as to ensure that they are fired at the appropriate time for the engine running conditions. The control circuit is powered by a constant voltage source which is normally at a lower voltage than that supplied to the primary side of the ignition circuit. Although these type of ignition circuits are very efficient and effective, certain types of them do have one feature which may be undesirable. That is, when the ignition switch is initially turned on, because of the way in which the ignition circuit is triggered, all of the spark plugs will be fired instantly and regardless of the condition of the engine.
Referring to FIG. 1, a conventional engine control unit is identified generally by the reference numeral 11. The engine control unit controls the timing of the ignition circuit 12. The engine control unit is equipped with a microcomputer 13 which is powered by a controlled constant voltage (+5 v) from the +12 v battery 14 at the time the ignition switch 15 is closed. The ignition timing signal cable 17 conducts the ignition control signal from the microcomputer 13 to the base of NPN switching transistor 16. The NPN switching transistor 16 functions as a switch. In the normal state the microcomputer generates a high level signal such that NPN switching transistor 16 functions as a closed switch. The collector of NPN switching transistor 16 is grounded and the input to the ignition circuit 12 is a low level signal such that no power is available to ignite the ignition circuit. In the ignition state the microcomputer 13 generates a low level signal such that NPN switching transistor 16 acts as an open switch and the power from the battery is connected to the ignition circuit 12 causing the engine to fire.
However the conventional engine control unit can cause engine misfiring. As soon as the ignition switch 15 is closed the microcomputer 13 is powered and begins initialization. The initialization causes a delay before the microcomputer 13 can generate the high level signal to the base of NPN switching transistor 16 over the ignition timing signal cable 17. During the delay a low level signal is present on the base of the NPN switching transistor 16 causing the NPN switching transistor 16 to act as a open switch. The battery power is connected to the ignition circuit for each ignition circuit in the engine. As a result all engine cylinders fire at the same time such that an engine misfire occurs before the engine is started.
It is, therefore, an object of this invention is to provide an improved engine control unit for an internal combustion engine.
It is a further object of this invention to provide an engine control unit with a delay circuit active at ignition switch closure wherein the connection between the battery power and the ignition circuit is delayed and wherein the delay is of sufficient time such that the microcomputer is able to generate the ignition control signal.